1. Field of the Invention
The present invention relates in general to an active vibration damping device for use in an automotive engine mount, body mount, or vibration suppression device, to provide active or offsetting damping action. More particularly, the present invention is concerned with a fluid filled active vibration damping device wherein a portion of the wall of a pressure receiving chamber with a non-compressible fluid sealed therein is constituted by an excitation plate, with the excitation plate being actuated by electromagnetic actuating assembly in order to control the pressure in the pressure receiving chamber, which forms the basis for the aforementioned damping action.
2. Description of the Related Art
A fluid filled active vibration damping device are known as one kind of vibration damping coupling or mount to be installed between components that are desired to be damped, such as an automotive engine mount or body mount, to provide vibration damped coupling between the components. A damping apparatus of this kind typically has a construction wherein a first mounting member and a second mounting member connected to one another by a rubber elastic body are respectively attached to the components to be coupled in vibration damping fashion, and comprising a pressure receiving chamber a portion of whose wall is constituted by the rubber elastic body, and having a non-compressible fluid sealed therein. An excitation plate constitutes another portion of the wall of the pressure receiving chamber, with pressure control of the pressure receiving chamber being carried out by means of excitation of the excitation plate by the actuating assembly. With this arrangement, for example, components coupled in vibration damping fashion are subjected to excitation corresponding to vibration to be damped, on the basis of which the vibration may be offset; or the spring characteristics of the mounting may be modified depending on input of vibration to be damped, to produce low spring or the like, in order to provide active damping action of the vibration.
In order to effectively achieve damping action with a fluid filled active vibration damping device of this kind, a high-level of control accuracy and responsiveness are required during pressure control of the pressure receiving chamber. For this reason, it is preferable to use electromagnetic actuating assembly, such as a voice coil type or electromagnet type employing a coil, as taught in JP-A-8-80751, JP-A-2000-227137, and JP-A-2002-188677.
For reasons relating to manufacture, in most cases, the electromagnetic actuating assembly is fabricated as a separate part from the rubber elastic body and the vibration damping device proper comprising the pressure receiving chamber and excitation plate, and installed in the vibration damping device with the output member of the actuating assembly coupled to the excitation plate.
In the fluid filled active vibration damping device of conventional construction as taught in the above described documents, when coupling the output member of the actuating assembly with the excitation plate, the output member and the excitation plate are bolted together; or the output member is secured press-fit into a cylindrical portion projecting from the excitation plate; or the output portion is positioned on a caulking portion provided to the excitation plate, and subjected to caulking. A resultant problem is that the coupling operation was both laborious and time consuming.
In the active vibration damping device of this kind, due to differences in dimension of components and sites pertaining to coupling of the output portion and the excitation plate, and to error (deviation) of mounting location of the electromagnetic actuating assembly on the vibration damping device proper, there is a risk that the center axis of the excitation plate and the center axis of the output member will be misaligned. If the components are forcibly coupled with their axes misaligned with one another, in addition to the risk of possible damage to the excitation plate, there is also the problem of the center axis of the excitation plate and the center axis of the output member becoming inclined relative to the vertical. Due to the fact that actuated displacement of the excitation plate is not realized efficiently, this makes it difficult to achieve the desired excitation force, and thus an inherent problem is that the desired damping action may not be achieved consistently.
Where it is attempted to establish a high degree of dimensional accuracy of components pertaining to coupling of the output portion and the excitation plate in order to address such problems, production and management become extremely difficult.